Process for the oxidation of leuco compounds of the triaryl methane series



Patented May 19, 1931 I l UNITED STATES PATENTIOFFICE KARL SCHMIDT, orLEVERKUSEN, GERMANY, ASSIGNOR To GENERAL nmnmnwonxs,

mo, on NEW YoRK, N. Y., A CORPORATION or DELAWARE PROCESS FOR THEOXIDATION or LEUCOGOMZEOUNDS on THE TRIARYL METI-IANE SERIES No Drawing.Application filed October 20, 1928, Serial 115313335, and in GermanyOctober as, 1927.

The present invention concerns the oXida-' tion of leuco compounds ofthe triarylmethane series by treating the leuco compounds in solution ofpyridine bases, such as pyridine or homologues thereof, quinoline andthe like or mixtures of these bases, with oxygen, with the addition of acopper salt.

In accordance with the invention leuco com pounds of dyestuffs of thetriarylmethane series can easily be oxidized to the correspondingdyestuffs, by reacting upon the leuco compounds dissolved in a pyridinebase, (such as pyridine, homologues or other substitution productsthereof, quinoline, lepidine, etc.) with oxygen in the presence of asuitable organic or inorganic copper salt such as cupricchloride,-sulfate, acetate, -formiate, -carbonate, -oxalate, cuprouschloride orthe like, whereby it is to be understood that in the term oxygen alsooxygen containing gases such as air are intended to be included. The

reaction is advantageously performed at temperatures between about 80120(3., the addition of suitable diluents such as water, methyl alcohol,ethyl alcohol, acetone, glycerine or the like being in some cases ofadvantage. The amount of copper salts to be added is a very smallone,for instance 2% and less, (calculated upon the leuco compound), beingoperable in most cases.

When working in this manner oxidation nerforms in a very convenientmanner and on a technical scale also in such cases, where otheroxidatlon methods heretofore known are inoperable or only yield smallamounts of the dyestuffs, which latter is, for instance,

the case with the dyestuffs mentioned in the examples of thisapplication.

The following examples illustrate my invention without limiting itthereto Ewample 1 while leading air through and heating to;

about100 Ciuntil the dyestufl'has complete. ly separated. After coolingthe dyestuff is filtered and any adhering-pyridine is removed w withsodium chloride solution. The yield of the dyestufl', the formula:

which probably corresponds to,

| SOaNB is almost quantitative. Instead ofthe cupric chloride othercopper salts, such as for'example, cuprous chloride, cupric sulphate orthe like can be used. V

The leuco acids obtainable from ortho toluidine andbenzaldehyde-2.4-disulphonicacid or para xylidine and benZaldehyde-QA-disulphonic acid can beoxidized equally satisfactorily following theabove directions.

, Ewample 20 'grams of para leucaniline or the corresponding. quantityof the mono-, dior trichloro hydrate thereof are dissolved in ccs. ofpyridine and 0.7 grams of cupric chlo ride, dissolved in 5 cos. ofwater, are added. The solution is treated as described in Ex ample 1. Assoon as the formation vof'the dyestuff is complete, the pyridine isdistilled off invacuo, the productis dissolved in dilute hydrochloricacidand the chlorohydrate .of

parafuchsine is precipitated with sodium chloride. The product isthenpurified by redissolving. The yield of dyestuifis very] the addition ofa little water.

satisfactory. The pyridine can be replaced by homologues thereof, byquinoline or by mixtures of these bases. The dyestuff, thus obtainable,probably corresponds to the formula:

raNO ONE,

NE: E trample 3 20 grams of the leuco acid obtained from orthocresotinic acid and benzaldehyde ortho sulphonic'acid according to theusual methods are dissolved in 130 cos. of pyridine with This solution,

after the addition of 1 gram of cupric chloride is heated to 100 C.while stirring rapidly and leading air through until the oxidation iscomplete. After distilling off the pyridine the dyestuff is salted outfrom the acid solution. In this case part of the pyridine can also'bereplaced by gylcerin'e. The dyestuif thus obtainable, probablycorresponds in its free form to the formula:

(3H1 Hs ooo 0 ooon l Us 0111 I claim:

1. Process which comprises dissolving a leuco compound of a dyestuif ofthe triarylmethane series in a pyridine base and oxidizing the leucocompound by means of oxygen in the presence of a suitable copper salt.

2. Process which comprises dissolving a leuco compound of a dyestuff ofthe triarylmethane series in a pyridine base and oxidizing the leucocompound at a temperature between about 80-120 0'. by means of oxygen inthe presence of a suitable copper salt.

3. Process which comprises dissolving a V leuco compound of a dyestufiof the triarylfrom vicinal meta xylidine and benzaldehyde-QAt-disulfonic acid, in pyridine and oxidizing the leuco compound inthis solution with oxygen in the presence of copper chloride at atemperature of about 100 C.

In testimony whereof I have hereunto set my hand.

KARL SCHMIDT. [us]

